Agrophysiological characterisation and parametrisation of Andean tubers: Potato (Solanum sp.), oca (Oxalis tuberosa), isaño (Tropaeolum tuberosum) and papalisa (Ullucus tuberosus)

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Europ. J. Agronomy 28 (2008) 526–540

Agrophysiological characterisation and parametrisation of Andean tubers: Potato (Solanum sp.), oca (Oxalis tuberosa), isa˜no (Tropaeolum tuberosum) and papalisa (Ullucus tuberosus) Bruno Condori a,1 , Pablo Mamani a,1 , Ruben Botello a,1 , Fernando Pati˜no a,1 , Andr´e Devaux b,2 , Jean Franc¸ois Ledent c,∗ a

Fundaci´on Para la Promoci´on e Investigaci´on de Productos Andinos, Casilla 1079, La Paz, Bolivia b Centro Internacional de la Papa, P.O. Box 1558, Lima 12, Peru c Unit´ e d’Ecophysiologie et d’Am´elioration V´eg´etale, Universit´e Catholique de Louvain, Croix du Sud, 2 bte 11, 1348 Louvain-la-Neuve, Belgium Received 28 June 2007; received in revised form 8 December 2007; accepted 10 December 2007

Abstract Bolivia is part of the eight most important centres of biodiversity and domestication of plants in the world, including a broad diversity of Andean grains, roots and tubers. A study was implemented to obtain the quantitative information to develop and validate, a simple growth potential model of Andean tubers in production areas located above 3000 m altitude, and to analyze the difference between species in growth attributes and the resulting tuber production. Three potato species and sub-species (Solanum tuberosum ssp. andigenum and ssp. tuberosum, and Solanum juzepczukii) as well as Oca (Oxalis tuberosa), Isa˜no (Tropaeolum tuberosum) and Papalisa (Ullucus tuberosus) were studied. Trials were conducted under normal field conditions prevailing in Bolivia but with the best cropping techniques available locally to obtain optimal growing conditions. Data on dry weight (of leaves, stems, tubers and roots) and leaf area were taken at several dates in five trials conducted between 1993 and 2003. The percentage of ground cover was also measured. Beta functions were fitted to data of dry weight and leaf area to establish growth curves. The potato groups have a smaller cycle duration than other Andean tubers. The Crop Growth Analysis indicated three important characteristics differentiating Andean tubers: the S. juzepczukii potato has a high Relative Growth Rate (RGR) and a higher leaf mass ratio but a smaller tuber yield, due to a smaller harvest index (HI) and a very low Net Assimilation Rate (NAR). S. tuberosum ssp. tuberosum potatoes have smaller Leaf Area Index (LAI), and RGR than juzepczukii, but their NAR and HI are higher. S. tuberosum potatoes are quite productive for the size of their LAI. The Tropaeolum tuberosum or Isa˜no has a great capacity of Ground Cover (GC) or a great LAI that is not translated into a greater tubers yield. It has low RGR, NAR and HI compared to all the other species studied. The crop growth was interpreted in Light Use Efficiency (LUE) and evolution of light interception through a linear model. The LUE of potato group is more elevated than the LUE of the other Andean tubers. Within each group there is no statistical difference for the LUE value. The relationship of LAI with GC or fraction of light interception was determined with both linear and exponential relations. The low slope value for the relationship between LAI and GC characterises all Andean tubers studied compared to results reported for potato under other latitudes. © 2007 Elsevier B.V. All rights reserved. Keywords: Native potato; Andean tuber; Growth analysis; Light use efficiency

1. Introduction ∗

Corresponding author. Tel.: +32 10 47 34 58; fax: +32 10 47 20 21. E-mail addresses: [email protected] (B. Condori), [email protected] (P. Mamani), [email protected] (R. Botello), [email protected] (F. Pati˜no), [email protected] (A. Devaux), [email protected] (J.F. Ledent). 1 Tel.: +591 22 141209. 2 Tel.: +511 349 6017. 1161-0301/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.eja.2007.12.002

Bolivia is part of the eight most important centres of biodiversity and domestication of plants in the world, including a broad diversity of Andean grains, roots and tubers. Amongst the tubers, the most widespread through the Andes since pre-Hispanic times are oca (Oxalis tuberosa Molina), isa˜no (Tropaeolum tuberosum Ruiz and Pav´on), papalisa (Ullucus tuberosus Caldas) and

B. Condori et al. / Europ. J. Agronomy 28 (2008) 526–540

potato (Solanum ssp. L.) (Contreras, 2001; Rea, 1998). Of these tubers, potato is the most known and grown over the world, followed by oca, even though oca is produced only in Mexico and New Zealand (CIED, 2002) outside the Andes. The other tubers are specific to the Andean highlands. Superficies of Andean tubers other than potatoes are not known with precision but in the regions where potatoes are in rotation with other Andean tubers the superficies should be approximately equal (potatoes and other Andean tubers). The composition and the number of varieties which constitute the Andean tubers germplasm is very heterogeneous and the quantities of seed material in collections is limited hence a risk of loss of biodiversity. The banks of germplasm kept in Toralapa (Bolivia) contain 1200 accesions of potato, 500 de oca, 200 de papalisa, and 80 de isa˜no (Garcia and Cadima, 2003). Except for isa˜no which is mainly used for feeding pigs Andean tubers are grown chiefly for human consumption under different forms (fresh, boiled, fried, oven cooked, stewed, as soups, meal obtained after dehydration, etc.). There is also some use as medicinal plants. Some studies on the nutritional value and rusticity of Andean tubers confirm them as alternatives to cover increasing demands in human and animal food and in industry, however, there is still little knowledge of the growth dynamics and potential production characteristics of such tubers (CIED, 2002). It is a known fact that Andean tubers played a multiplicity of roles in human activities since pre-Hispanic times; however, at present such tubers are almost forgotten and therefore underused, with the exception of potato (NRC, 1989; Tapia, 1994; Rea, 1998). Bolivia has a broad diversity of cultivated and wild potatoes, 7 and 31 species, respectively, as noted by Ochoa (1990). But of the seven species cultivated, three can be cited as more important. In order of importance and market presence, the sub-specie Solanum tuberosum ssp. andigenum with the Waycha cultivar should be cited as one of the variety most appreciated by the consumers, both rural and urban. It is followed by Solanum juzepczukii with the bitter cultivar Luki and Solanum tuberosum ssp. tuberosum with the cultivars Alpha and Desir´ee (Irigoyen, 2002). Due to its high concentration of glycoalkaloids, Luki has a bitter taste when consumed fresh without processing (Ochoa, 1990). For this reason it is processed into a frozen and dehydrated product called chu˜no or tunta before consumption, using a traditional processing method. One of its favourable attributes is that it can be grown in the highest areas (at elevations over 3000 m) due to its tolerance to frost (Rea, 1992). Alpha is a cultivar introduced from Europe, it is better adapted to milder areas, with the advantage of a shorter cycle, it becomes a winter production alternative in semi-tropical regions of Bolivia, even though its presence in the market is relatively recent and still small (Irigoyen, 2002). It is noteworthy that in Bolivia compared to other Andean countries, the yield of tuber crops, potato included, is low in spite of the rusticity of the species and varieties used and even though they are genetic resources from this region (OEA, 1996). This could be due to several factors, such as the technological, socioeconomic and cultural factors. Another factor is the poor

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knowledge about the growth and production processes of the Andean tubers (Tapia, 1994; Zeballos, 2006). Most national statistics or authors mention potato as the tuber of reference and only in very specific occasions oca and papalisa are mentioned. Official reports indicate that mean domestic yields of fresh tubers are about 6 t/ha for potato, 3 t/ha for oca and 4 t/ha for papalisa (Montes de Oca, 1992; Tapia, 1994; Zeballos, 1997, 2006; INE, 1999). No official reports on isa˜no yields are available, though some studies indicate that isa˜no yields can be quite higher than potato yields (CIED, 2002). However, in other research reports, values higher than the national mean can be found: Gonzales et al. (1997) indicate means of 25 t/ha of tubers for potato and oca, and 30 t/ha for isa˜no in farmers plots of the Candelaria area, a agrobiodiversity zone in Cochabamba. Other researchers, such as Iriarte (2003, personal communication), indicate that in communities close to the area surrounding Lake Titicaca yields of 27–31 t/ha of oca, and 38–41 t/ha of isa˜no can be found. Quispe et al. (1997) reports yields of 30 t/ha of potato, 22 t/ha of oca and 33 t/ha of isa˜no. Reports on isa˜no yields are noteworthy, since yields ranging from 9 to 74 t/ha can be found (Grau et al., 2003). Research reports on papalisa indicated that its yield could reach 33 t/ha (Garcia and Cadima, 2003). This gap between maximum yields and average yields shows the necessity to consolidate a clear and accurate knowledge based on the characterisation of Andean tubers, describing the main agrophysiological indices to determine their growth under average and optimal conditions, and thus understand their functioning. This could serve to establish criteria of genetic improvement for the development of cultivars, criteria of crop management and parameters to be used in simulation systems for improving the crop management and thus achieving better yields. One way in which development and growth dynamics in plant species can be studied and explained is through Crop Growth Analysis, an explanatory, holistic and comprehensive approach to interpret plant form and function (Clawson et al., 1986; Hunt, 1982; Hunt et al., 2002). Growth analysis techniques are based on a description of the physiological performance of a species, considering that the accumulation of carbon is determined by the amount of foliage and their daily photosynthetic efficiency. Some studies on the growth and production of Andean tubers have addressed specific aspects according to the objective of each study, such as phenology, fertilization, and hydroponics, both in Bolivia (Quispe et al., 1997; Valdivia et al., 1998) and Peru (Valladolid et al., 1984; Gomez et al., 2001) using growth analysis techniques. The above studies used different methodologies, such as “classic” growth analysis (Hunt, 2003) or “functional” analysis of growth according to Hunt (1979, 1982) and Hunt et al. (2002), where polynomial equations are fitted to values of the coordinates of points measured through time to obtaine trend values. The coefficients of these equations cannot be biologically explained; moreover, Poorter (1989) indicates that such growth curves may exhibit erratic behaviours. A relatively recent alternative to plot growth curves is the Beta function proposed by Yin et al. (2003). It is presented as one of the most versatile functions to describe growth curves and to

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use for agronomic interpretation and characterisation purposes, because plotting of such curves requires three parameters clearly explainable and easily measurable in the field. This function makes an easier description and interpretation of a crop growth analysis (CGA). Considering the above, this study is intended to characterise and analyze different Andean tubers through the comparison of their agrophysiological attributes and their growth dynamics under their natural agroecological conditions. In another paper the growth model for native potato species will be analyzed. 2. Materials and methods 2.1. Genetic material For this study, three genotypes of potato, one of oca, one of isa˜no and one of papalisa were used. For potato, the species and sub-species studied were: S. juzepczukii (JUZ) with the bitter cultivar Luki; Solanum tuberosum ssp. andigenum (AND) with the cultivar Waycha; Solanum tuberosum ssp. tuberosum (TUB) with the cultivar Alpha. In oca or O. tuberosa (OXA) the cultivar Puka˜nawi was used. In Isa˜no or T. tuberosum (TRO) the cultivar Anaranjado was used. In papalisa or U. tuberosus (ULL) the cultivar Manzana was used; these potato, oca, isa˜no and papalisa cultivars are the most widespread amongst farmers of the studied area. 2.2. Trials For the growth and development study of Andean tubers several trials were conducted in Toralapa, Candelaria and Patacamaya, in Bolivia (Table 1). The trials were conducted in experimental stations (Toralapa and Patacamaya) and in farmers fields (Candelaria) but in all cases there was a cooperation between researchers and local farmers for the cultivation and crop management. The crops were managed according to the best local cropping techniques. Toralapa is located at an elevation of 3430 m, at 17◦ 30 SL and 65◦ 40 WL. The average temperature in this location is 11 ◦ C, relative moisture 55%, and annual rainfall 500 mm. Candelaria is located at an elevation of 3265 m, 17◦ 16 SL and 65◦ 66 WL. The average temperature in this location is 11 ◦ C, relative moisture is 80%, and rainfall

950 mm (CIDETI, 1994). Patacamaya is located at an elevation of 3800 m, at 17◦ 14 SL and 67◦ 55 WL. The average temperature in this zone is 11.2 ◦ C, with relative moisture 50%, and rainfall 385 mm (Montes de Oca, 1992). The station of Patacamaya closed in 2000 but it was still in activity at the time of these trials. In these areas the potato is usually the first crop of the rotation system. In Patacamaya and Toralapa potatoes are planted after a rest period (fallow) of 2–3 years, but in Candelaria, because the cropping system is more intensive there is no fallow period. In the three locations, the Andean tubers come always as third or fourth crop in the rotation after potato, quinoa, and faba bean. During the trial implementation, cropping techniques included fertilization, weeding, ridging and preventive phytosanitary treatments to ensure plant health and obtain the maximum yield under these conditions. Planting density was 47,600 plants per hectare, with distances of 0.7 m between furrows and 0.30 m between plants. For fertilization, 80–160–0 to 80–160–60 kg/ha of N, P2 O5 and K2 O were applied, based on soil requirements, and additional irrigation was also used as required and as available (e.g., additional irrigation was performed in Patacamaya). The planting dates were the same for the different Andean tubers but the harvest date was established according to maturity and development cycle of the Andean tubers tested (Table 1). Pests and diseases treatments against late blight (Phytophthora infestans (Mont. de Bary) were applied using Mancozeb + metalaxil (Ridomil MZ) and Clorotalonil (Bravo 500), Andean weevil (Premnotrypes latithorax Pierce, Premnotrypes solaniperda Kuschel, and Rigopsidius tucumanus Heller) and moth (Phthorimaea operculella Zeller, Symetrischema tangolias Gyen, Paraschema detectendum Povoln´y) by synthetic cipermetrine-based pyrethroids (Karate) and clorpirifos (Lorsban). Experimental plots for each trial were arranged in complete randomised blocks with three or four repetitions, the surface area of each experimental plot ranged from 21 to 29.4 m2 (Table 1). 2.3. Data collection Daily measurements of maximum and minimum temperatures, global solar radiation and rainfall were recorded using

Table 1 Description of the trials conducted to study the growth curves of Andean tubers Trial

Elevation (m)

Mean temperaturea (◦ C)

Species studied

Planting date

Harvest date

Cycle (days)

Number of harvests

Plot × repetition

Soil typeb

Toralapa Patacamaya Toralapad Candelaria Candelaria

3430 3800 3430 3265 3260

11.4 11.1 11.5 11.0 11.4

TUB, AND, JUZc TUB, AND, JUZ OXA, TRO OXA, TRO, ULL OXA, TRO, ULL

22/10/1993 19/10/1998 18/10/1995 16/10/1998 19/09/2003

13/04/1994 20/04/1999 08/05/1996 30/05/1999 27/04/2004

174 184 204 227 221

6 5 9 5 5

29.4 m2 × 4 21.0 m2 × 4 26.3 m2 × 4 24.0 m2 × 3 21.0 m2 × 3

SL SL SL L SL

a

Air temperature data are mean data from emergence to harvest. SL, silty loam. L, loamy. SL, sandy loam. c Species and sub-species of potato: JUZ is Solanum juzepczukii; AND is Solanum tuberosum ssp. andigenum; TUB is Solanum tuberosum ssp. tuberosum. Other Andean tubers: OXA is Oxalis tuberosa, TRO is Tropaeolum tuberosum and ULL is Ullucus tuberosus. d Part of the data of this trial were published by Quispe et al. (1997). b

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automatic or manual weather climate measurement equipment located on experimentation sites. Periodical sampling of biomass was performed five to nine times from emergence to final harvest, according to the availability of plants to be destroyed (Table 1). Harvests or samplings were determined based on four phenological macro-stages. Thus, the first harvest was determined at the onset of foliage formation upon completion of plant emergence; the second harvest was made at the onset of tuberisation and flowering whereas the third one occurred at the maximum development of foliage and physiological maturity. The last harvest took place when plants had at least half of their foliage in senescence and their tuber skin fully set. In each experimental unit and in each sampling, the fresh and dry weights of four plants fractioned in leaves (L), stems (S) and tubers (T) were measured. The sum of L plus S gives foliage weight (Sh). The sum of Sh plus T is the total biomass (W). Leaf Area Index (LAI) was measured using an area meter (LICOR, model LI-3000A, Lincoln, USA). The LAI is the ratio of the foliar surface per unit of soil surface. Root (R) weight was measured but not included in the total plant weight, due to its variability caused by the difficulty of separating roots from the soil. Root growth is only taken into account to calculate its proportion in the total biomass. The ideal size of potato samples has been reported to be of six to nine plants for studies on nitrogen concentration (Goffart et al., 2000), a coefficient of variation (CV) from 4 to 8% being obtained in that case. In this study, the plant samples were only used to determine the dry matter concentration. The ground cover (GC) of leaf canopy was also measured. This corresponds to the portion of soil surface hidden by the canopy when seen from above. These readings were made periodically, every 15 days, from emergence to a short time before the harvest, using a mesh grid of 100 rectangles of 7 cm × 9 cm, obtained from the multiple of the distance between furrows and the distance between plants, respectively. The ground cover data was taken to estimate directly the crop capacity to intercept light during the vegetative cycle (Haverkort et al., 1991). 2.4. Data analysis 2.4.1. Final yield of total biomass and tubers The last harvests of each cropping cycle were used to calculate the fresh tuber yields (FTY in t/ha). The dry tuber yield (DTY in kg/ha) was determined from the fresh yield using the percentage of dry matter in tubers (DMT in %). The Harvest Index (HI) was determined by the ratio of DTY to total dry matter (TDM in kg/ha). 2.4.2. Crop growth analysis In Crop Growth Analysis, three main aspects will be presented: the accumulation of biomass in the different plant organs; the distribution of assimilates generated by each part of the plant (stems and leaves versus tubers); the estimates of the different absolute and relative rates and indices of the CGA itself. A summary of the parameters and variables of this study is described in Table 2.

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Table 2 Abreviations, list of variables and parameters used in the growth analysis Abbreviation

Description

Units

A AGR CGA Cm

Leaf area Absolute growth rate Crop growth analysis Maximum value of the absolute growth rate Dry matter concentration in tubers Dry tuber yield Fresh tuber yields Ground cover Harvest index Leaf weight Leaf area index Leaf area ratio Leaf mass rate Light use efficiency Net assimilation rate Photosynthetically active radiation Root weight Relative growth rate Stem weight Shoot weight Specific leaf area Tuber weight Total dry matter Total plant weight (with out roots) Any growth parameter (W, T, Sh, R)

m2 /m2 g/day, Eq. (3) – g/m2 , Eq. (2)

DMT DTY FTY GC HI L LAI LAR LMR LUE NAR PAR R RGR S Sh SLA T TDM W Y

% kg/ha t/ha Fraction % g/m2 m2 /m2 m2 /g, Eq. (6) × Eq. (7) g/g, Eq. (7) g/MJ g m−2 day−1 , Eq. (5) MJ/m2 g/m2 g g−1 day−1 , Eq. (4) g/m2 g/m2 m2 /g, Eq. (6) g/m2 kg/ha g/m2 g/m2 , Eq. (1)

Inside parenthesis is the number of reference attributed in the text to the equation used for calculating the parameter or variable.

To construct the Beta-curves of accumulated biomass, we started with primary yield data (W, T, Sh, R) measured over time in several intermediate harvests, as described in data collection. Every data set (W, T, Sh, R) was subjected to a non-linear regression analysis to obtain the growth curves over time expressed in days on a surface area of 1 m2 of soil. The regression was based on the Beta function (Yin et al., 1995, 2003), a more versatile and explanatory equation than a polynomial equation commonly used for CGA. The Beta function is of a sigmoid type with three clearly explanatory parameters, and based on two fundamental equations (Eqs. (1) and (2)):   te /(te −tm )  t te − t Y = Ymax × 1 + × , te − t m te with 0 ≤ tm < te  Cm = Ymax ×

2te − tm te × (te − tm )

(1) 

 ×

tm te

tm /(te −tm ) (2)

Y is any growth parameter; t is the time in days after emergence; tm is the time when the maximum growth rate of Y is reached; te is the time when the growth period ends. Ymax is the maximum value of Y reached at te time (Eq. (1)). Cm is the maximum value of the absolute growth rate reached at tm time (Eq. (2)). The Beta regression was calculated with the Sigma Plot software (Evaluation Version 8.02) that calculates non-linear regression through iterations, and requires an initial approximate value for each parameter of the function.

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Assimilates distribution, was characterised by the proportion of dry matter allocated in the different organs, leaves, stems and tubers, and its evolution through time was determined using the Beta-curves. The CGA (crop growth analysis) was based on the curves fitted to the Beta function: with total plant weight (W in g/m2 ), leaf area (A in m2 /m2 ), or leaf weight (L in g/m2 ) as dependent variable. Using these curves the following growth parameters were determined: the Absolute Growth Rate (AGR) based on Eq. (3): the Relative Growth Rate (RGR) based on Eq. (4); the Net Assimilation Rate (TAN) by Eq. (5); the Specific Leaf Area (SLA) by Eq. (6); the Leaf Mass Rate (LMR) by Eq. (7). The Leaf Area Ratio (LAR) can also be determined by the product of Eqs. (6) and (7). These parameters have been discussed in several research works conducted since the turn of the century and are still used nowadays. Hunt (1982), Clawson et al. (1986) and Hunt et al. (2002) discuss their limitations and scope in detail. dW (g/day) dt     1 dW RGR = × (g g−1 day−1 ) W dt     dW 1 × (g m−2 day−1 ) NAR = A dt

AGR =

SLA =

A L

LMR =

L W

(3) (4)

(5)

(m2 /g)

(6)

(g/g)

(7)

2.4.3. Measurement of the photosynthetic mechanisms and light use efficiency of the plant Evident relationships between LAI and GC exist for potato crop, and these range from a linear relationship to an exponential relationship (Haverkort et al., 1991; Tourneux et al., 2003; Jefferies and Mackerron, 1989; Kooman, 1995). To determine whether or not the different species of Andean tubers show a relation to LAI, which is consistent with the models determined for potato, we conducted regression analyses on LAI and GC, pairing the data observed throughout the whole growth cycle of the crops. On the other hand, we determined light use efficiency (LUE) for each species of Andean tubers. This was performed by a linear regression analysis of the amount of intercepted photosynthetically active radiation (PAR) and the total dry biomass produced over time. The PAR was calculated from global radiation data. The light interception fraction is measured directly by GC and can serve to estimate the accumulated value of the intercepted PAR, as explained by Haverkort et al. (1991). Studies conducted on potato all over the world demonstrate an average value of 2.8 g of dry matter for each MJ of intercepted light (Stol et al., 1991). The LUE value for the other Andean tubers remains unknown to this day. The program used for these analyses was also Sigma Plot (Evaluation Version 8.02).

3. Results and discussion Fig. 1(A) shows the final yield for the fresh tubers (FTY) of various Andean species. In general, isa˜no (TRO) shows the highest yield (55 t/ha) of all species, whereas papalisa (ULL) shows the lowest one (26 t/ha). Oca (OXA) has an average yield of 31 t/ha similar to potato. Amongst potatoes, the yields of andigenum (AND) with 35 t/ha, and tuberosum (TUB) with 34 t/ha, do not differ significantly among them but both are statistically higher than the yield of juzepczukii (JUZ), with 31 t/ha. Dry matter concentration in the tuber (DMT) (Fig. 1(B)), differs significantly amongst the species. Broadly speaking, the potato group has the highest dry matter concentration (over 23%), JUZ has the highest DMT value in the group, 33%, whereas for AND the intermediate DMT value of 26% is reached. Amongst the other Andean tubers, ULL has a percentage of 18% dry matter, OXA has a value of 15% and TRO shows the lowest dry matter concentration in the tuber (8%). A higher concentration of dry matter is known to be associated with better quality for processing or industrial uses. JUZ and AND have the highest dry matter yield (TDM), followed by TUB (Fig. 1(C)). Other Andean tubers, TRO and OXA have higher dry yields than ULL, but these three tubers have lower yields than the potato group. A trend in the total yield (TDM) and dry tuber yield (DTY) is found in the potato group, where differences, are found between JUZ, AND and TUB (in decreasing order of yield). In the other tubers, dry yield of OXA, ULL and TRO do not differ significantly (Fig. 1(C)). In this case too, the yield of these three Andean tubers is quite lower than in the potato group. These lower yields may be due to the capability of translocation of assimilates to the tuber characteristic of each species and expressed by the Harvest Index. The above statement can be explained by the harvest index HI (DTY/TDM ratio), which differs significantly among species. In the potato group, TUB shows the highest HI value, with 86%, followed by JUZ with 78% and AND with 67%. HI values of 70% and 61% are observed for ULL and OXA, respectively, and the lowest value is found in TRO, with 42% (Fig. 1(D)). Potatoes and other Andean tubers have been found to be highly productive species, meaning that the largest portion of the entire production of biomass, goes to tuber production, except in TRO. Indeed their HIs are over 61%. This is higher than in other species of worldwide importance for food, such as grains (about 50%) or oil-seeds (about 35%) as Kooman (1995) mentions. The results for these five agronomic variables may be close to optimal or potential levels for the production systems where the trials were implemented. Indeed these data were gathered in trials minimizing stress caused by factors that can be affected by crop management (moisture, pests and soil fertility) and under low population density with 100% emergence (47,600 plants/ha). In actual conditions of field production, the first factor that affects yields negatively is the seed heterogeneity, both in size and quality that results in an emergence rate below the planting density, crop heterogeneity and causes direct losses in the final yield. Climatic constraints affect plant performance in general and this applies also to emergence. In the trials conducted, the average emergence was 80%, even though selected

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Fig. 1. Agronomic behaviour of Andean potatoes: S. t. ssp. tuberosum (TUB), S. juzepckzukii (JUZ) and S. t. ssp. andigenum (AND); other Andean tubers: Oxalis tuberosa (OXA), Tropaeolum tuberosum (TRO) and U. tuberosus (ULL); in (A) fresh tuber yield in t/ha (FTY); (B) percentage of dry matter in tubers (DMT); (C) total dry matter and dry tuber yield in kg/ha (TDM and DTY); (D) harvest yield (HI). Mean of the values observed in the final harvest, error bars were determined by all trials for each species. S. t. is Solanum tuberosum.

seed of certified quality had been used. Our plots appeared more homogeneous (compared to some farmers plots) but we are aware that in field plots of homogenous appearance the samples corresponding to small surface areas can generate an overestimation up to 30% (Ledent, 2005 personal communication). Despite this possible overestimation our results show that a more rigorous management allows achieving yields several times higher than the yields reported in statistics and bibliography (Table 3). Relative yield was obtained by dividing the value of these potential yields (Fig. 1(A)) by the domestic mean (Montes de Oca, 1992; Tapia, 1994; Zeballos, 1997; INE, 1999) or by the mean of local data or trials conducted for research purposes (Garcia and Cadima, 2003). Our results allowed deducing some relations or ratios between total dry biomass (TDM) and dry tuber yield (DTY)

and between dry tuber yield (DTY) and fresh tuber yield. These ratios were obtained across environments and cultivars. These ratios although approximate may be useful to estimate biomass or dry tuber yield when only fresh tuber yield is available. 3.1. Dry biomass accumulation The means observed for biomass (g/m2 ), i.e., total dry weight without roots (W = T + Sh), tubers (T), shoots (Sh = leaves + stems) and roots (R) were subjected to a nonlinear regression analysis over time (days) by the Beta function. The three parameters of this function are descriptive, because they provide the value of the maximum growth rate at different times. They help us interpret the duration of the cropping cycle (Table 4). Determination coefficients r2 show a high fit of the

Table 3 Final yield on the trials for each Andean tuber, relative yields vis a vis potential yield, and two constants of production units’ transformation Andean tuber species

TUB JUZ AND OXA TRO ULL

Final yield (t/ha)

34.4 31.3 34.9 30.5 56.2 25.3

Relative yields

Transformations

On the national mean

On mean local data

From TDM to DTY

From DTY to FTY

6.88 6.26 6.98 10.17 – 6.25

1.64 1.49 1.66 2.03 4.01 1.67

×0.86 ×0.78 ×0.67 ×0.61 ×0.42 ×0.70

×4.30 ×3.00 ×3.88 ×6.63 ×12.99 ×5.78

No official reports on the national yield of isa˜no (TRO) are available. See Fig. 1 for abbreviations. TDM is total dry matter, DTY is dry tuber yield and FTY is fresh tuber yield.

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Table 4 Beta parameters and coefficients of determination for biomass accumulation in diverse organs of Andean tubers fitted by the Beta function TUB Total weight (W = T + Sh) Cm 17.70 Wm 1071.00 67 tm te 104 0.96 r2 Tubers (T) Cm Tm tm te r2

19.67 951.34 74 104 0.94

Shoots (Sh = L + S) 4.16 Cm 211.24 Shm tm 35 te 75 0.79 r2 Roots (R) Cm Rm tm te r2

0.16 10.12 40 90 0.42

S.E.

JUZ

S.E.

AND

S.E.

OXA

S.E.

TRO

S.E.

ULL

S.E.

1.3 11.6 0.6 0.9

17.41 1007.82 70 104 0.94

0.9 8.02 1.2 1.9

18.48 1102.76 68 104 0.90

2.3 26.5 1.6 2.3

9.00 662.27 95 137 0.88

0.7 73.2 5.9 17.0

10.81 873.64 100 147 0.86

0.3 32.0 2.6 1.5

8.43 557.55 75 115 0.94

0.5 51.6 9.0 15.9

**

0.4 3.8 0.2 0.3 **

0.3 19.4 7.4 2.9 **

– – – – ns

23.33 659.01 90 104 0.90 8.24 435.85 45 82 0.77 0.53 29.48 45 85 0.40

**

0.1 14.9 0.6 1.2 **

0.8 52.4 20.1 13.9 **

– – – – ns

18.53 792.83 78 104 0.86 7.16 385.25 45 83 0.79 0.53 30.76 40 85 0.35

**

0.2 21.6 1.4 2.3 **

0.5 33.8 6.5 2.6 **

– – – – ns

10.38 460.86 118 137 0.88 3.88 259.12 70 112 0.72 0.18 11.44 70 110 0.30

**

0.2 18.9 1.9 4.9 **

0.2 17.4 19.7 11.9 **

– – – – ns

7.81 401.77 115 147 0.86 8.81 573.96 85 122 0.69 0.70 39.56 90 120 0.38

**

0.2 16.3 2.1 2.8 **

0.2 17.6 4.6 2.1 **

– – – – ns

9.74 431.27 95 115 0.83 3.64 206.13 55 92 0.71 0.21 11.10 55 89 0.23

**

0.1 15.3 1.5 3.8 **

0.1 5.9 3.4 1.4 **

– – – – ns

Where S.E. is the Standard Error; ns is r2 not significant. W is the total weight of the plant, T is the weight of the tubers, Sh is foliage weight, and R is root weight; all expressed in dry weight and g/m2 . t is the time in days after emergence; tm is the time when the maximum growth rate of W (T, Sh or R) is reached; te is the time when the growth period ends. Wmax is the maximum value of W (T, Sh or R) reached at te time. Cm is the maximum growth rate reached at time tm expressed in g m−2 day−1 . ** r2 highly significant.

Beta function for the different parts of the plants, except the roots. Fig. 2 provides the growth curves for each Andean tuber organ and species. By way of example, we show the points observed for the total dry matter (W), where we have a high r2 (over 0.86 in all species). This analysis allows a more accurate description of the cropping cycle duration, both in days and in thermal time (base 0 ◦ C, Squire, 1995), considering a daily mean temperature of 11 ◦ C, accumulated as from emergence. This figure shows root growth, which is very reduced relative to the growth of other parts of the plant. Total root extraction was limited in each sampling due to: sample extraction depth, involuntary cuts or breaking of roots due to the presence of gravel in the soil, losses during sample washings; for that reason R data was not considered in the total biomass sum. Fig. 2 shows the bars of Standard Error (S.E.) that compare the sampling of the species inside potato group and the other Andean tubers. To avoid filling the figure, and to make a simple presentation we showed the S.E. at three stages, at the beginning of the accumulation of biomass, at the maximal velocity of growth and in the final phase of accumulation of biomass. These stages are reached at 62, 102 and 144 DAP for the potato group and at 90, 133 and 177 DAP for the other Andean tubers (with slight variations of days). The S.E. bars are are given for these dates in the figures presenting CGA (Figs. 4 and 5).

Four macro-stages or phenological phases (Kooman and Haverkort, 1995) were identified by the values of the parameters of the Beta function and the fitted curves (Table 5). Phase 0 of emergence, covers the period of time from planting to emergence, determined by direct periodical counts of the population emerged over the total plants planted. This phase is considered reached when half of the population has emerged and takes 40–60 days, depending on the species (Table 5). Phase 1, of onset of tuberisation goes from emergence to the onset of tuberisation when the biomass of tubers reaches 1 g/m2 as calculated by the Beta function. Leaf development occurs mainly in this phase, that lasts 22–65 days depending on the species and includes the onset of tuberisation, which requires 253–726 ◦ C days (base temperature of 0 ◦ C) depending on the species (Table 5). Phase 2, of maximum total growth rate goes from the onset of tuberisation to the maximum growth rate of total biomass, which coincides with the maximum accumulation of dry matter in foliage, which phase is reached from 748 to 1056 ◦ C days or from 107 to 150 days after planting (Table 5). Phase 3, of senescence goes from the maximum growth rate of foliage to the end of the cropping cycle or to senescence, and corresponds to 1144–1628 ◦ C days (Table 5). This phase is reached when at least half of the foliage is senescent and

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Fig. 2. Dynamic of dry matter accumulation; observed values (circles) and curves fitted to observed values with Beta function in total biomass plant (solid line), tubers (dotted line), shoots (dashed line) and roots (dashed–dot–dot line). Andean potatoes: S. t. ssp. tuberosum (A; TUB), S. juzepckzukii (B; JUZ) and S. t. ssp. andigena (C; AND) and the other Andean tubers: Oxalis tuberosa (D; OXA), Tropaeolum tuberosum (E; TRO) and Ullucus tuberosus (F; ULL). DAP is days after planting. Tt0 is thermal time with a base temperature of 0 ◦ C; Tt0 is accumulated of mean temperatures (11 ◦ C per day) from emergence.

when the total growth and tuber curve reaches its asymptote plateau (Fig. 2). The final harvest usually takes place after an additional lag period following that phase, because at that time the tuber skin is not yet well fixed This tuber maturity period

allows the formation of a periderm which helps to prevent losses due to physical damages during harvest and storage. Such waiting period can involve 30 additional days for potatoes (Tavares, 2002).

Table 5 Phenological phases duration of the diverse species of Andean tubers in days after planting, days after emergence and in thermal time (base 0 ◦ C) Species

TUB JUZ AND OXA TRO ULL

Emergence

Onset of tuberisation

Maximum total growth rate

DAP (E.S.)

DAP (S.E.) [DAE]

◦ C day

40 (0.142) 40 (0.055) 40 (1.732) 55 (1.155) 45 (2.309) 60 (1.444)

62 (1.453) [22] 76 (1.732) [36] 70 (2.309) [30] 120 (1.590) [65] 105 (1.155) [60] 105 (2.603) [45]

253 407 341 726 671 505

Senescence

DAP (S.E.) [DAE]

◦ C day

DAP (S.E.) [DAE]

◦ C day

107 (0.577) [67] 110 (0.882) [70] 108 (1.155) [68] 150 (0.667) [95] 145 (1.738) [100] 135 (0.945) [75]

748 781 759 1056 1001 891

144 (1.392) [104] 144 (0.581) [104] 144 (2.485) [104] 192 (1.392) [137] 192 (2.028) [147] 175 (2.887) [115]

1144 1144 1144 1518 1628 1276

Values based on the Beta-fitted curves in Fig. 2. DAP is days after planting and, S.E. is Standard Error, [DAE] is days after emergence. ◦ C day is the thermal time based on 0 ◦ C.

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Fig. 3. Proportion of dry matter distributed daily between tubers, stems and leaves. Values obtained from Beta-curves. DAP is days after planting. Tt0 is thermal time wit h a base temperature of 0 ◦ C; Tt0 is accumulated of mean temperatures (11 ◦ C per day) from emergence.

3.2. Distribution of assimilates Fig. 3 shows the model of daily distribution of assimilates between the different organs such as leaves, stems and tubers relatively to the total. This model was based on the values fitted with the Beta function and the phenological phases described above. In general, the distribution of assimilates to the tubers in OXA, TRO and ULL takes longer and is slower (100 DAP) than in potatoes (TUB, JUZ, and AND at 60 DAP). In potatoes, TUB is the first to start the process of translocation to the tubers, which is sustained over time. In all cases but OXA, leaves make up most of the plant fraction in the initial phenological phase, whereas in OXA the proportion of leaves and stems is almost the same during the initial phase. 3.3. Crop growth analysis Several absolute and relative growth rates or growth attributes in Andean tuber species were obtained with CGA, includ-

ing AGR, LAI, SLA (Fig. 4) and RGR, LMR and NAR (Fig. 5). In the first place, the general trends of curves of AGR and LAI present similarities in all cases and they differ little among species (Fig. 4(A, B and D, E) although there are some differences as explained below. No differences in the maximum value of AGR were observed in potato, whereas in JUZ and AND LAI values higher than in TUB were found. Even though TUB has a lower LAI, the value of its AGR is not the lowest (Fig. 4(A and B)). This could be indicative of a greater efficiency of allocation of assimilates per leaf area for TUB compared to the other two species. In the potato species the maximum values of AGR and LAI are reached at the same time. Among the other Andean tubers, TRO has a higher AGR and a markedly higher LAI value than OXA and ULL. By contrast, ULL has the lowest LAI value, but its AGR is not very different from the AGR in OXA. Again, this could be explained by a lower light use efficiency in TRO and OXA, and a better light

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Fig. 4. Functional Crop Growth Analysis for Andean potatoes (A–C): S. t. ssp. tuberosum (TUB, solid lines), S. juzepckzukii (JUZ, dotted lines) and S. t. ssp. andigena (AND, dashed lines); the other Andean tubers (D–F): Oxalis tuberosa (OXA, solid lines), Tropaeolum tuberosum (TRO, dotted lines) and Ullucus tuberosus (ULL, dashed lines). Absolute Growth Rate (AGR, g/day), Leaf Area Index (LAI, m2 /m2 ), and Specific Leaf Area (SLA, m2 /day). Values obtained from dry weight and leaf area data fitted with Beta function. DAP is days after planting. Tt0 is thermal time with a base of 0 ◦ C; Tt0 is accumulated of mean temperatures (11 ◦ C per day) from emergence.

use by ULL. The maximum values of AGR and LAI are reached at different times in each species (Fig. 4(D and E)). As compared to the potato group the other Andean tubers appear in general, to require a longer time to reach the maximum AGR and LAI values. Only TRO reaches a maximum LAI similar to that of JUZ and AND potatoes; OXA has a LAI similar to that of TUB. However, all AGR values of the other Andean tubers are much lower than those of the potato group (Fig. 4(A, B and D, E)). SLA values (Fig. 4(C)) tend to remain constant (plateau) during a major part of the cropping cycle, it changes only at the beginning (when it increases) and at the end of growth (when it decreases); the SLA values are higher for JUZ and AND than for TUB, ranging from 0.023 to 0.020 m2 /g. In comparative terms, all tubers species other than potatoes reach SLA values lower

than those of potatoes. The maximum SLA values in species other than potatoes are reached by OXA and ULL, with 0.020 and 0.018 m2 /g, the lower SLA value being found in TRO, with a maximum value of 0.013 m2 /g. Fig. 5 shows the evolution of RGR, LMR and NAR, through time. No major differences between species can be found, except for differences in the times at which they reach their highest values. These values drop at first abruptly and then slowly. In potato, this drastic drop is reached 60 days after emergence whereas in the other tubers the drop occurs at 80 DAE. Difference in the RGR value among species at the beginning of the growth cycle (Fig. 5(D)) is observed only among the Andean tubers other than potatoes. There are no significant statistical differences between the potatoes, however among other Andean tubers TRO shows the lowest RGR (Fig. 5(A and D)).

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Fig. 5. Functional Crop Growth Analysis for Andean potatoes (A–C): S. t. ssp. tuberosum (TUB, solid lines), S. juzepckzukii (JUZ, dotted lines) and S. t. ssp. andigena (AND, dashed lines); the other Andean tubers (D–F): Oxalis tuberosa (OXA, solid lines), Tropaeolum tuberosum (TRO, dotted lines) and Ullucus tuberosus (ULL, dashed lines). Relative growth rate (RGR, g g−1 day−1 ), Leaf mass ratio (LMR, g/g) and Net assimilation rate (NAR, g m−2 day−1 ). Values obtained from dry weight and leaf area data fitted with Beta function. DAP is days after planting. Tt0 is thermal time with a base of 0 ◦ C; Tt0 is accumulated of mean temperatures (11 ◦ C per day) from emergence.

LMR is considered as the capacity of the plant to invest in potentially photosynthetic parts (leaves). Among the potatoes JUZ has a higher LMR value and therefore invests in more foliar mass, contrary to TUB and AND (Fig. 5(B)) which invest more in tubers. Other tubers do not differ in LMR at the beginning of the cycle but as the cycle advances differences occur TRO is presenting more foliage for the production of the same given total biomass (Fig. 5(E)). NAR relates to the capability of mass production by unit of leaf surface area. In terms of NAR the potato TUB is the most efficient although the differences with the other tubers are not always clearly marked (Fig. 5(C)). Potatoes evolution of NAR follows a similar tendency as the other tubers but with a greater duration of evolution through the time (Fig. 5(F)).

A global analysis including several parameters (growth rates, etc.) obtained from CGA, shows that rates change according to the moment and the species. Comparison of their values can be done at given fixed moments such as at the end (final value) or at a point near the maximum (at 102 DAP for potatoes and 133 DAP for other Andean tubers) (Table 6). The potato TUB has a greater capacity for biomass production per surface unit area (NAR) than JUZ and AND. A lower proportion of foliar biomass in the total plant mass is found for TUB compared to JUZ and AND. The thickness of leaves (1/SLA) is lower for TUB (P < 0.05) than for AND and JUZ. These characteristics (lower NAR, smaller SLA) are associated with a lower RGR resulting in a lower efficiency in the generation of total biomass. However, JUZ presents a high RGR

B. Condori et al. / Europ. J. Agronomy 28 (2008) 526–540 Table 6 Comparison of the values of the Relative Growth Rate (RGR), Net Assimilation Rate (NAR), Leaf Mass Ratio (LMR) and Specific Leaf Area (SLA), for the 102 DAP in potatoes and 133 DAP for other Andean tubers Species

RGR (g/g) = NAR (g/m2 ) × LMR (g/g) × SLA (m2 /g)

TUB JUZ AND E.S.

0.032 0.035 0.033 (0.0010)

6.65 4.39 5.04 (1.67)

0.23 0.35 0.28 (0.03)

0.021 0.023 0.024 (0.0007)

OXA TRO ULL S.E.

0.031 0.026 0.027 (0.0018)

4.27 3.57 4.67 (0.32)

0.34 0.54 0.30 (0.07)

0.022 0.013 0.019 (0.0024)

The data come from the curves of Figs. 4 and 5. S.E. is the Standard Error between the species of potato and other Andean tubers, respectively.

but with a greater allocation of assimilates to the leaves (LMR), which could affect negatively the tuber yields. TRO presents a smaller NAR than the others (OXA and ULL) but with a very high LMR, a low SLA and a low RGR similar to ULL. In spite of having a high LAI, TRO allocates more assimilates to the foliage that to the tubers (Table 6). 4. Measurements of the photosynthetic mechanisms of the plant and light use efficiency 4.1. Relationship between LAI and GC The relationships between LAI and GC (ground cover) have been studied by several authors. Exponential type functions, proposed by Jefferies and Mackerron (1989), Kooman (1995), are presented for reference purposes in Fig. 6. Other researchers such as Haverkort et al. (1991) and Tourneux et al. (2003) established a linear relationship between LAI and GC, determining that GC equals one-third of LAI (for LAI values ≤ 3). The fraction of intercepted light was found to be equal to GC obtained by measurements of the ground cover with a grid or leaf canopy

537

Table 7 Mean values of the coefficients of the exponential function resulting from the regression between LAI and GC proposed by Jefferies and Mackerron (1989), and Kooman (1995) Species

Coefficients of the function y = a − c × exp(−bx) and coefficient of determination a

c

b

R2

TUB JUZ AND OXA TRO ULL

0.50 (0.13) 0.70 (0.35) 0.85 (0.44) 0.70 (0.49) 1.00 (0.25) 0.50 (0.33)

0.51 (0.12) 0.75 (0.32) 0.90 (0.40) 0.73 (0.46) 1.01 (0.23) 0.54 (0.31)

0.96 (0.78) 0.45 (0.46) 0.38 (0.37) 0.40 (0.46) 0.36 (0.19) 1.18 (1.41)

0.88 0.90 0.87 0.81 0.90 0.89

General

1.00 (0.21)

1.01 (0.20)

0.29 (0.10)

0.86

Standard Error values appear in brackets.

intercepting light (Haverkort et al., 1991). The purpose of these relationships is to determine, by LAI measurements or simple measurements of GC the fraction of light intercepted, with which we can subsequently find the amount of photosynthetically active radiation intercepted by the plants. Table 7 shows the coefficients obtained by regression when fitting the exponential function y = a − c × exp(−bx) where: y is GC; a is the maximum value of GC; c is the intercept of the relation log(y − a) on x; b is the curve’s slope or the coefficient of extinction; x is the LAI. In broad terms, it can be established that, of the values of coefficients a and c are quite close to each other, as also indicated in the bibliography (Jefferies and Mackerron, 1989). Such a result is also quite logical since we expect y = 0 for x = 0. The value of a (maximum value reached by GC) is considered to be a characteristic of each species. Thus, TRO reaches a maximum GC value of 1, whereas the lowest of these values is found in the TUB potato and in ULL, with a maximum GC value of 0.5. The highest values of b, are found for ULL (1.18) and TUB (0.96), i.e., their coefficient of extinction related to LAI (−b × LAI) is lower than in the other species where it ranges

Fig. 6. Relationship between ground cover (GC) and LAI (leaf area index) Exponential relationship (dotted line with GC = 1 − 1.021 × exp−0.29 × LAI ) and linear relationship (dashed line with GC = 1/5 × LAI, R2 = 0.87) between GC and LAI from observed values in Andean tubers. Relationship obtained by Kooman (1995) is GC = 1 − 1 × exp−1 × LAI and by Jefferies and Mackerron (1989) is GC = 0.93 − 1.03 × exp−0.746 × LAI .

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Fig. 7. Relationship between intercepted PAR (MJ/m2 ) and total dry matter (kg/ha). Dashed line corresponds to LUE for Andean potatoes (2.69 g/MJ) and dotted line to LUE for the other Andean tubers (1.52 g/MJ).

from 0.36 to 0.45, the lowest value of b being observed for TRO and potato AND. The coefficients of determination corresponding to these regressions reach values higher than 0.81. When we cease to apply the GC limit per species, that is a = 1, and merge all the species in a single data cloud, we obtain the general function shown in Table 7 and applicable to all Andean tubers. Fig. 6 shows the distribution of the observations points of LAI and GC used to fit the general function for all species. Coefficients a and c tend to the value of 1, coinciding with Kooman (1995) and to what is logically expected as mentioned above. By contrast the slope is lower than the value of 1 reported for instance by Kooman (1995), reaching a value of 0.29. Large differences occur between this general value and the values obtained separately by species. The slope of the relationship between LAI and GC is lower than in Kooman (1995) or Jefferies and Mackerron’s (1989) theoretical function. This may be explained by the mean temperature at which the trials were conducted (11 ◦ C daily mean), which is significantly different from the t temperatures between 17 and 25 ◦ C under which the work of these other researchers was conducted. These temperatures may have promoted a faster leaf development, something that does not occur in the areas of production of Andean tubers. This faster development may have influenced plant architecture and favoured more horizontal leaves, more opened plants (leaning stems) and therefore a higher extinction coefficient. In our conditions the opposite could have occurred resulting in lower extinction coefficient and lower ground cover for a given LAI. Such differences in architecture are also observed among species in our trials. For instance, TUB and ULL have a low LAI but the same GC value as species with a higher LAI in the initial part of the curve and they appear to have an angle of foliar insertion more horizontal but in absence of precise determination of canopy architecture features this remains speculative. When all species were subjected to a linear regression analysis, the simple relationship GC = LAI/5 with R2 = 0.87 was found, which is different from the relation GC = LAI/3 (Fig. 6) found by Haverkort et al. (1991) and Tourneux et al. (2003).

4.2. Light use efficiency The relation between accumulated data of intercepted PAR and total dry matter produced was studied by a linear regression analysis, as shown in Fig. 7. The intercepted PAR was determined by the product of GC by PAR and accumulated through the cropping cycle (Haverkort et al., 1991). The slope of the regression line corresponds to light use efficiency. The slopes for each species were compared; few variations among potatoes or among the other Andean tubers were found, but there was a marked superiority of potatoes relatively to the other species (potatoes presented higher slope). Thus, data were grouped and two new different regression lines were calculated: one for the potato group and the other one for the other tubers. The LUE value for the potato group was 2.69 g/MJ and the LUE for oca, papalisa and isa˜no was found to be 1.51 g/MJ (expressed on the basis on dry matter). The LUE found for potatoes is close to values reported by other researchers (Stol et al., 1991; Kooman and Haverkort, 1995). Thus, compared to potatoes, the other Andean tubers have a lower LUE, a smaller maximum GC and GC values close to the maximum values are maintained only for a short duration of time Maximum GC values were 0.6 and 0.4 for OXA and ULL, respectively. All of them but TRO fail to achieve complete GC (GC values do not reach 1), their NAR is low (Fig. 5(F) and Table 6) and the resulting productivity is small. 5. Conclusions We characterised the agrophysiological behaviour of Andean tubers and quantitatively determined their growth dynamics under the climatical constraints encountered in the different sites of experiment which can be considered as representative of the typical zones where Andean tubers are grown. Our objective was not to study in details the impact of variations in these climatical constraints or the effects of specific events such as frosts or (as in Tourneux et al., 2003) water stress. Significant differences between species were found for their agronomic characteris-

B. Condori et al. / Europ. J. Agronomy 28 (2008) 526–540

tics such as yield, harvest index and dry matter concentration in tubers. Tuber yields were clearly above the national figures commonly reported; this is due to the optimum management conditions of the trials. Isa˜no has a higher fresh tuber yield than the other Andean tubers, including potato, however, it should be mentioned that this apparent advantage results from the large amount of water that isa˜no accumulates in its tubers with only 8% of dry matter. When the tuber dry yields of isa˜no and of other Andean tuber species such as oca and papalisa, are compared they do not differ despite the lower harvest index of isa˜no. The tuber dry yield of isa˜no is lower than in the potato species analyzed. Isa˜no has presented the lowest harvest index. The potato group has the highest harvest index; the S. juzepczukii potato is the highest in terms of total dry matter yield. The Beta function proved to be useful for fitting and analyzing growth curves. In general, the growth of potatoes and other Andean tubers present similar trends; the specific difference is the longer time taken by the other Andean tubers in each phenological phase. The Crop Growth Analysis indicated three important characteristics differentiating the Andean tubers: the S. juzepczukii potato compared to other tubers species has a higher relative growth rate but a smaller tuber yield, due to a smaller harvest index associated to a high leaf mass ratio and a very low net assimilation rate (NAR). The S. tuberosum sp. tuberosum potato has a smaller leaf area index (LAI), an higher tuber yield although their RGR is lower, and their NAR is very high. With a smaller utilisation of assimilates in foliage and a high harvest index S. tuberosum sp. tuberosum is the most productive subspecie in relation to its relatively low LAI. Differences among these species may be related to their origin; the tuberosum used in this study is an improved variety selected for its yield capacity in higher latitudes and temperate conditions while the juzepczukii is a native crop that adapted itself over the years to the adverse climatic conditions of the Andes (frost and drought). T. tuberosum or Isa˜no has a great capacity of ground cover by foliage and a great LAI that is not translated in a greater tubers yield, it has low RGR, NAR and harvest index as compared to all the other species studied. In addition its allocation of biomass to the leaves is high as indicated by its leaf mass ratio. A linear and exponencial relationship were determinated; the coefficients of the fitted equations vary especially on the slopes among the species of Andean tubers. The slopes of the equation describing the relationship between LAI and GC (light interception fraction) values are lower in the tubers grown in the Andes as compared to the values reported for potato elsewhere due to lower local temperatures (11 ◦ C average), and probably to the architecture of the Andean tuber plants (high stems and horizontal dispositions of leaves). The value of light use efficiency, found for the potato variety used in this study was similar to those reported in the bibliography for potatoes. The other Andean tubers have lower LUE values. A high tuber yield is not only determined by a high LUE. The lower HI values found for Andean tubers contributed also to their lower yield. Duration of light interception or maintenance of maximum LAI values tended to be lesser in our conditions, characters of the foliar system such as high LAI, low SLA and LMR). also played a role in some cases to explain the differences

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of yield obtained but not systematically (higher LAI were not necessarily associated with higher yields and vice versa). This characterisation of agrophysiological parameters and the development of growth of Andean tubers will be useful for a better knowledge, to improve their management and to build a simple model of these traditional crops for the region. Testing the behaviour of the different tubers under the stress conditions commonly found in the regions of cultivation remains to be conducted. Acknowledgements The field experiments in Bolivia were conducted with the team of researchers of Foundation Proinpa. ‘The Universit´e catholique de Louvain, UCL, Belgium’ attributed a fellowship to B. Condori. The International Potato Centre CIP contributed through the projects Papa Andina y ALTAGRO to the finalisation and revision of this paper. The authors thank all those who made this work possible. References CIDETI, 1994. Diagn´ostico socioecon´omico de la Microregi´on de Tiraque. Volumen 1. Poblaci´on, Historia social y organizaci´on. Comit´e Interinstitucional para el desarrollo de Tiraque, Cochabamba-Bolivia. CIED (Centro de investigaci´on educaci´on y desarrollo), 2002. Productos Andinos potenciales. Online at: http://www.ciedperu.org/productos/fraprod.htm. Clawson, K.L., Spetch, J.L., Blad, B.L., 1986. Growth analysis of soybean isolines differing in pubescence density. Agron. J. 78, 164–172. Contreras, A., 2001. Ecofisiologia del rendimiento de la planta de papa. Faculdad de Ciencias Agrarias de la Un iversidad Austral de Chile. Online at: http://www.agrarias.uach.cl/webpapa/pag04.html. Garcia, W., Cadima, X. (Eds.), 2003. Manejo sostenible de la agrobiodiversidad de tub´erculos andinos: S´ıntesis de investigaciones y experiencias en Bolivia. Conservaci´on y uso de la biodiversidad de ra´ıces y tub´erculos andinos: Una d´ecada de investigaci´on para el desarrollo (1993–2003). Fundaci´on para la Promoci´on e Investigaci´on de Productos Andinos (PROINPA). Alcald´ıa de Colomi, Centro Internacional de la Papa (CIP). Agencia Suiza para el Desarrollo y Cooperaci´on (COSUDE), Cochabamba, Bolivia, 208 pp. Goffart, J.P., Olivier, M., MacKerron, D.K.L., Postma, R., Johnson, P., 2000. Spatial and temporal aspects of sampling of potato crops for nitrogen analysis. In: Haverkort, A.J., MacKerron, D.K.L. (Eds.), Management of Nitrogen and Water in Potato Production. Wageningen Pers, Wageningen, pp. 83– 102. Gomez, D., Rodriguez-Delfin, A., Fernandez, E., 2001. An´alisis de crecimiento de plantas de Mashua (Tropaeolum tuberosum) sometidas a condiciones nutricionales marginales. Anales cient´ıficos de la UNALM. Lima, Peru 47, 280–296. Gonzales, S., Almanza, J., Devaux, A., Condori, P., 1997. Zonas productoras de tub´erculos andinos, identificaci´on e investigaci´on de factores limitantes de producci´on y conservaci´on en Cochabamba. In: Universidad Nacional de San Antonio Abad del Cusco (UNSAAC), Centro de Investigaci´on en cultivos Andinos (CICA), Asociaci´on Arariwa (Eds.), IX Congreso Internacional de Cultivos Andinos. Cochabamba, Bolivia, p. 21. Grau, A., Ortega Due˜nas, R., Nieto Cabrera, C., Hermann, M., 2003. Mashua (Tropaeolum tuberosum Ruiz & Pav.). Promoting the Conservation and Use of Under-utilized and Neglected Crops, vol. 25. International Potato Center/International Plant Genetic Resources Institute, Lima, Peru/Rome, Italy. Haverkort, A.J., Uenk, D., Veroude, H., Van de Waart, M., 1991. Radiation interception by potato canopy: relations between ground cover, intercepted solar radiation, leaf area index and infrared reflectance of potato crops. Potato Res. 34, 113–121.

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